A variety of the information, such as audio or video information, is converted into digital signals and handled as digital data, and hence may readily be handled by for example a personal computer or by a mobile computer. The above information may be compressed in bandwidth by an audio codec or video codec technology so as to be distributed by digital communication or digital broadcast to a variety of communication terminal equipment readily efficiently. For example, audio/video data (AV data) may be received outdoors by portable telephone sets.
The transmitting/receiving system for e.g., AV data has come to be variably used through the proposal of a network system usable in a small local area, including households. As the network system, the next-generation wireless radio communication systems of the 5 GHz range as proposed for example in IEEE 802.11a, wireless radio LAN system of the 2.45 GHz range as proposed for example in IEEE 802.11b or in the near-distance wireless communication system, termed Bluetooth, is now stirring up notice.
The transmitting/receiving system for e.g., data exploits the wireless network system effectively to enable exchange of variable data, access to the Internet or transmission/reception of data in variable locations, such as in households or outdoors, conveniently without the interposition of relaying devices.
In a transmitting/receiving system for e.g., data, development of a communication terminal equipment which is small-sized, lightweight and portable and which has the above-mentioned communication functions, is essential. In communication terminal equipment, high frequency analog signals need to be modulated/demodulated in the transmission/reception section. Thus, there is usually provided a high frequency transmission/reception circuit 100 by the superheterodyne system in which transmission/reception signals are once converted from the transmission/reception signals into signals of the intermediate frequency, as shown in FIG. 1.
The high frequency transmission/reception circuit 100 includes an antenna unit 101 having an antenna or a changeover switch for receiving or transmitting information signals and a transmission/reception switching unit 102 for switching between transmission and reception. The high frequency transmission/reception circuit 100 also includes a reception circuit unit 105 made up by a frequency conversion circuit section 103 and a demodulating circuit section 104. The high frequency transmission/reception circuit 100 includes a transmission circuit unit 109 made up by a power amplifier 106, a drive amplifier 107 and a modulating circuit section 108. The high frequency transmission/reception circuit 100 also includes a reference frequency generating circuit unit for supplying the reference frequency to the reception circuit unit 105 and to the transmission circuit unit 109.
The above-described high frequency transmission/reception circuit 100 is made up by an extremely large number of component parts, not shown in detail. These include large-sized functional parts, such as filters introduced between different stages, a local oscillator (voltage controlled oscillator or VOC), a SAW (surface acoustic wave) filter and passive component parts, such as inductance, resistance or capacitance components peculiar to high frequency analog circuits, including matching and bias circuits. Thus, the high frequency transmission/reception circuit 100 is large-sized in its entirety to prove hindrance to reduction in size and weight of the communication terminal equipment.
In communication terminal equipment, a high frequency transmission/reception circuit 110 by a direct conversion system, adapted for transmitting/receiving information signals without conversion to the intermediate frequency, as shown in FIG. 2, is also employed. In the high frequency transmission/reception circuit 110, the information signals, received by an antenna unit 111, are supplied via a transmission/reception switching unit 112 to a demodulating circuit unit 113 for direct baseband processing. In the high frequency transmission/reception circuit 110, information signals generated in a source are directly modulated in a modulating circuit unit 114, without conversion to an intermediate frequency, so as to be transmitted from an antenna unit 111 through an amplifier 115 and the transmission/reception switching unit 112.
In the above-described high frequency transmission/reception circuit 110, in which information signals are transmitted/received by direct detection without converting the information signals into intermediate frequency signals, the number of component parts, such as filters, may be reduced to simplify the overall structure to achieve a structure close to one chip. However, the high frequency transmission/reception circuit 100 needs to be matched to filters or matching circuits arranged on the downstream side. In the high frequency transmission/reception circuit 110, since the signals are amplified at a time in a high frequency stage, it becomes difficult to achieve a sufficient gain, so that the amplifying operation needs to be performed in the baseband unit. Thus, the high frequency transmission/reception circuit 110 is in need of a circuit for canceling DC offset, or redundant low-pass filters, thus further increasing the overall power consumption.
The conventional high frequency transmission/reception circuit is not of sufficient characteristics to satisfy required specifications, such as reduction in size or weight of the communication terminal equipment, whether the circuit is of the superheterodyne type or the direct conversion type. Thus, in the high frequency transmission/reception circuit, various attempts are being made for designing the circuit as a module with a small size by a simplified structure based on for example an Si-CMOS circuit. One of such attempts is to form passive devices of optimum characteristics on an Si substrate and to build a filter circuit or a resonator on an LSI (large-scale integrated circuit) and to integrate a logic LSI of the baseband section in an IC to produce a so-called one-chip high frequency substrate.
In this one-chip high frequency circuit substrate, it is crucial how to form an inductor unit 120 of high performance, as shown in FIGS. 3A and 3B. In this high frequency circuit substrate, a large recess 124 is formed in register with an inductor unit forming portion. 123 of an Si substrate 121 and an SiO2 insulating layer 122. In this high frequency circuit substrate, a first wiring layer 125 is formed facing a recess 124, while a second wiring layer 126 is formed on the SiO2 insulating layer 122 to form a coil section 127. In the high frequency circuit substrate, a wiring pattern may, alternatively, be lifted from the substrate surface in air to form the inductor unit 120.
This high frequency circuit substrate suffers a problem that the inductor unit 120 has to be formed by numerous cumbersome process steps, thus raising the cost. Moreover, in the high frequency circuit substrate, the electrical interference between the high frequency circuit section of the analog circuit and the baseband circuit section of the digital circuit poses a serious problem.
As a high frequency circuit substrate, a high frequency circuit substrate 130, employing an Si substrate, shown for example in FIG. 4, or a high frequency circuit substrate 140, employing a glass substrate, shown in FIG. 5, has been proposed.
The high frequency circuit substrate 130, shown in FIG. 4, is arranged so that, with the use of an Si substrate as the base substrate 131, an SiO2 layer 132 is formed on this base substrate 131, and a passive device layer 133 is formed by for example a photolithographic technique. Although not shown, a passive device unit 135, such as an inductor unit, a resistance unit or a capacitor unit, is formed in multiple layers, along with a wiring layer 134, through an insulating layer 136, in the inside of the passive device layer 133 of the high frequency circuit substrate 130, in a manner not shown in detail.
In the high frequency circuit substrate 130, a terminal section 137, connected to the wiring layer 134, is formed through e.g., a via-hole on the passive device layer 133. On this terminal section 137, there are mounted functional devices 138, such as high frequency ICs or LSIs, by for example a flip chip mounting method. With the high frequency circuit substrate 130, the high frequency circuit section is separated from the baseband circuit section, by mounting on e.g., a motherboard, for preventing electrical interference between the two circuits.
Meanwhile, if, with the high frequency circuit substrate 130, the passive device unit 135 is to be formed within the passive device layer 133, the base substrate 131, which is an electrically conductive Si substrate, tends to interfere with optimum high frequency characteristics of the passive device unit 135.
On the other hand, in a high frequency circuit substrate 140, shown in FIG. 5, a glass substrate is used as the base substrate 141, in order to overcome the problem of the base substrate 131 in the high frequency circuit substrate 130 described above. A passive device layer 142 is formed by for example a photolithographic technique on the base substrate 141 of the high frequency circuit substrate 140. Although not shown, a passive device unit 144, such as an inductor unit, a resistance unit or a capacitor unit, is formed in multiple layers, along with a wiring layer 143, through an insulating layer 145, in the inside of the passive device layer 142 of the high frequency circuit substrate 140, in a manner not shown in detail.
In the high frequency circuit substrate 140, a terminal section 146, connected to the wiring layer 143, is formed through e.g., a via-hole on the passive device layer 142. On this terminal section 146, there are directly mounted functional devices 147, such as high frequency ICs or LSIs, by for example a flip chip mounting method. In this high frequency circuit substrate 140, an electrically non-conductive glass substrate is used as the base substrate 141 to suppress the capacitive coupling between the base substrate 141 and the passive device layer 142 to form the passive device unit 144 of optimum high frequency characteristics within the passive device layer 142. In this high frequency circuit substrate 140, a terminal pattern is formed on the surface of the passive device layer 142, for mounting on e.g., a motherboard, and connection to the motherboard is made by for example a wire bonding method.
In these high frequency circuit substrates 130, 140, high-precision passive device layers 133, 142 are formed on the base substrates 131, 141, as described above. In forming the passive device layer as a thin film, the base substrates 131, 141 need to exhibit thermal resistance against rise in the surface temperature during sputtering and contact alignment properties during masking, and to hold depth of focus during the lithographic processing.
Thus, the base substrates 131, 141 are required to be flat with high precision and to exhibit insulating properties, thermal resistance or resistance against chemicals. The base substrates 131, 141, formed as Si or glass substrate, exhibits these properties, thus enabling formation of an inexpensive low loss passive device by a separate process from the LSI forming process.
In the high frequency circuit substrates 130, 140, passive devices may be formed to a higher precision on the base substrates 131, 141 than is possible with the pattern forming methods by printing as used in the conventional ceramic module technique or with the wet etching methods used for forming a wiring pattern on the printing wiring board. Additionally, the device size can be reduced to approximately one hundredth of the area of the base substrate. Moreover, with the high frequency circuit substrates 130, 140, in which an Si substrate or a glass substrate is used as the base substrates 131, 141, the use limit frequency of the passive device may be increased to 20 GHz or higher.
In these high frequency circuit substrates 130, 140, patterns for high frequency signals, interconnections for supplying the power or providing ground connection or interconnection for control signals maybe achieved through the wiring layers 134, 143 formed on the base substrates 131, 141 described above. Thus, in the high frequency circuit substrates 130, 140, such problems may be produced as electrical interference across respective wirings, increased cost due to multi-layered wirings or bulkiness in size due to layout of the interconnections.
In the high frequency circuit substrates 130, 140, the cost is raised further due to use of a relatively expensive Si or glass substrate for the base substrates 131, 141.
In the high frequency circuit substrates 130, 140, the surfaces of the insulating layers 136, 145 become irregular due to thicknesses of the subjacent wiring layers 134, 143 to render it difficult to form the wiring layers 134, 143 or via-holes to a high accuracy on the surfaces of these irregular surfaces of the insulating layers 136, 145. In the high frequency circuit substrates 130, 140, since the surfaces of the insulating layers 136, 145 are irregular patterning images of the wiring layers 134, 143, the patterning images of the wiring layers 134, 143 or the via-holes become de-focused when the wiring layers 134, 143 or the vias are formed in the insulating layers 136, 145 using a photosensitive material, to render it difficult to form the wiring layers 134, 143 or the via-holes with high precision.
The high frequency circuit substrates 130, 140 are formed by mounting high frequency module unit 150 on a motherboard 151, as described above, as shown in FIG. 6. Here, the high frequency circuit substrate 130 is taken as an example.
In the high frequency module unit 150, the high frequency circuit substrate 130 is mounted on a major surface of the motherboard 151, as shown in FIG. 6. Moreover, the high frequency module unit 150 is sealed in its entirety by a shield cover 152 of, for example, an insulating resin. In the high frequency module unit 150, the pattern interconnections and input/output terminal units are formed on the front and back sides of the motherboard 151, while a large number of lands 153 are formed around the loading area for the high frequency circuit substrate 130.
In the high frequency module unit 150, the high frequency circuit substrate 130 is mounted on the motherboard 151 and, in this state, the wiring layer 136 of this high frequency circuit substrate 130 and the lands 153 are interconnected with wires 154 of the wire bonding method to supply the power or signals to the high frequency circuit substrate 130. Meanwhile, the high frequency circuit substrate 140 is mounted in similar manner to the motherboard 151.
In this high frequency module unit 150, including the shield cover 152 for sealing the functional devices 138, such as high frequency ICs or LSIs, loaded on the high frequency circuit substrate 130, it is a frequent occurrence that heat evolved from the functional devices 138 is confined in the shield cover 152 to deteriorate the operating characteristics.
In the high frequency module unit 150, in which the base substrate 131 of the high frequency circuit substrate 130 is an Si substrate, it is difficult to provide a heat dissipating structure to the base substrate 131. Moreover, since the passive device layer 133 is provided through the base substrate 131 on the motherboard 151, the device becomes bulky in size along its thickness.
Moreover, in the high frequency module unit 150, it is difficult to provide a wiring structure in the base substrate 131 of the high frequency circuit substrate 130 and hence a large number of the lands 153 are provided therearound for supplying the power, with the consequence that the device is increased in size in the planar direction.